1. Field of the Invention
The present invention relates generally to a semiconductor device and, more particularly, to a semiconductor device in which initial breakdown voltage deficiency of an insulating film is improved. The present invention also relates to an improved semiconductor device so that the amount of slight leak at a junction can be reduced.
2. Description of the Background Art
A single-crystal silicon substrate pulled up by the Czochralski process (hereinafter "CZ process") has been conventionally used for a MOS structure consisting of an upper electrode, an insulating film, and a semiconductor substrate, for a MOS field effect transistor (hereinafter "MOSFET") with source/drain regions formed at the both ends of the MOS structure, and for a semiconductor device or the like having a p-n junction diode. However, a silicon wafer obtained by the CZ process gets mixed, when a crystal is growing, with oxygen mainly from a quartz crucible used as a container which accommodates silicon melt. Therefore, the silicon wafer contains oxygen of not less than 10.sup.18 atoms/cm.sup.3 (old ASTM (Old American Society for Testing and Materials) value) and a silicon of higher purity has not been obtained.
Since conventional semiconductor devices are formed on substrates which are formed by the CZ process, the devices have been affected by defects caused by oxygen contained in the silicon substrates. Particularly, this oxygen has been troublesome in reliability as it affects Time Dependent Dielectric Breakdown (TDDB) characteristics of the gate oxide film and hot carrier effects. It is required to use low supply voltage in MOSFETs as they are miniaturized, and therefore, the thickness of gate oxide films has become thinner and thinner. Thus, declined reliability due to oxygen has become an increasingly serious problem.